ORIGINAL: ttoks
i fail to see how running the engine rich will hurt it, there is no way to over compress one a engines when it's shimmed right for the fuel your using, no matter how rich you run it the engine will flood before it get to that point, and then the only thing thats in danger is your glow plug not the engine, you must run the engine rich during break in because there is a lot of friction during break in from the tight fit of the piston and sleeve that creates a lot of heat, so you need the extra fuel to both lubricate the engines and to keep it cool.
Uh huh... I've seen half a dozen stretched out or cracked con-rods at the crank pin. It ALWAYS has happened in the first gallon of fuel, and often during the break-in period. With a combination of having the best possible pinch when new, and the extra volume of space taken up in the cylinder from the extra fuel, you certainly can overcompress an engine. I don't believe its an easy thing to do, but it can be done from the results I have seen.
This is not to say that you should not run rich during break in, because you should! You do need the extra lubrication. I think common sense, as well as the now infamous Steven Bess heat cycling article, would dictate a happy medium between the two opposing sides here.